Abstract
The development wells at the Ursa tension leg platform (TLP) site use 8.625" production casing in conjunction with 5.5" tubing to achieve the highest daily production rates to date in the Gulf of Mexico. The desire for large diameter production casing and the small margin between mud weight and fracture gradient at the deepwater Ursa site combine to require drilling a larger sized hole than the drift diameter of the previous casing string for all of the casing intervals. Bi-center bits have successfully drilled all of the intervals in one run except the section to total depth (TD). The last 1,000’ true vertical depth (TVD) on the first two wells were drilled and then under reamed prior to running casing.
The directional plan for the third well at the Ursa TLP included an 86° turn in azimuth and building hole angle to horizontal by 18,300’ TVD. The previous lack of success drilling the TD interval in one trip with bi-center bits led to using a 9.5" bit below a 6.75" AutoTrak rotary steerable closed loop system (RCLS) in combination with an 11.4" ream-while-drill (RWD) sub. This bottom hole assembly (BHA) would simultaneously drill and ream the hole to the proper diameter, thus eliminating the separate under-reamer run.
During the initial pilot hole penetration of the target reservoir and two subsequent sidetracks to build to horizontal, the RCLS / RWD system drilled approximately 20,000’ of Miocene age sand and shale sediments at inclinations that ranged from 30° to 88°. The instantaneous and average rate of penetration (ROP) increased 30% and 85% respectively over that achieved in the TD interval on the previous wells drilled with steerable mud motors and bi-center bits. The directional target of the well was intersected at the desired inclination and azimuth. Caliper logs obtained while evaluating the pilot hole showed the shales had been opened to the gauge diameter of
11.4" while the sands were opened to a slightly smaller diameter. Subsequent laboratory tests showed that the slightly smaller hole diameter in the sands was most likely due to filter cake build-up and/or barite sag.
This paper will discuss the planning, results, problems, and lessons learned during the first simultaneous use of rotary steerable and RWD technology while drilling a build to horizontal section to 18,300’ TVD on the Ursa A-6 well.
